Transcript Nondestructive inspection

Mechanical - D
Group - 8
Enrollment Numbers :1. 140020119597
2. 140020119598
3. 140020119599
4. 140020119600
5. 140020119601
Guided By:- H.N. JOSHI
Definition
A wide group of analysis techniques used in science and
industry to evaluate the properties of a material,
component or system without causing damage.
Nondestructive examination (NDE)
Nondestructive inspection (NDI)
Nondestructive evaluation (NDE)
Application Areas
• Aerospace engineering
• Mechanical engineering
• Electrical engineering
• Civil engineering
• Systems engineering
• Medicines
Methods of NDT
Visual
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Importance of NDT
1. NDT increases the safety and reliability of the product
during operation.
2. It decreases the cost of the product by reducing scrap and
conserving materials, labor and energy.
3. It enhances the reputation of the manufacturer as a
producer of quality goods. All of the above factors boost the
sales of the product which bring more economical benefits
for the manufacturer.
4. NDT is also used widely for routine or periodic
determination of quality of the plants and structures during
service.
5. This not only increases the safety of operation but also
eliminates any forced shut down of the plants.
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Six Most Common NDT
Methods
1.
2.
3.
4.
5.
6.
Visual Testing (VT)
Dye Penetrant Testing (DPT)
Magnetic Particle Testing (MPT)
Ultrasonic Testing (UT)
Eddy Current Testing (ECT)
Radiography Testing (RT)
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Visual Testing
Visual testing is the most basic and common inspection method
involves in using of human eyes to look for defects. But now it
is done by the use special tools such as video scopes,
magnifying glasses, mirrors, or borescopes to gain access and
more closely inspect the subject area.
Visual Testing Equipments:
•Mirrors (especially small, angled mirrors),
•Magnifying glasses,
•Microscopes (optical and electron),
•Borescopes and fiber optic borescopes,
•Closed circuit television (CCTV) systems,
•Videoscope.
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Visual Testing Equipments
Fig: Videoscope
Fig: Advanced Videoscope
Fig. Microscope
Fig: Borescopes
Fig: Magnifying glass
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Ultrasonic Testing
This technique is used for the detection
of internal surface (particularly distant
surface) defects in sound conducting
materials. In this method high
frequency sound waves are introduced
into a material and they are reflected
back from surface and flaws. Reflected
sound energy is displayed versus time,
and inspector can visualize a cross
section of the specimen showing the
depth of features.
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Basic Principle of Ultrasonic
Testing
A typical UT system consists of several functional units, such as
the pulser/receiver, piezoelectric transducer, and display devices. A
pulser/receiver is an electronic device that can produce high voltage
electrical pulses. Driven by the pulser, the transducer generates
high frequency ultrasonic energy. The sound energy is introduced
and propagates through the materials in the form of waves. When
there is a discontinuity (such as a crack) in the wave path, part of
the energy will be reflected back from the flaw surface. The
reflected wave signal is transformed into an electrical signal by the
piezoelectrical transducer and is displayed on a screen.
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Basic Principle of Ultrasonic
Testing
In the figure below, the reflected signal strength is displayed
versus the time from signal generation, when a echo was
received. Signal travel time can be directly related to the
distance. From the signal, information about the reflector
location, size, orientation and other features can sometimes be
gained.
initial
pulse
Piezoelectric
Transducer
crack
echo
back surface
echo
crack
0
2
4
6
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Oscilloscope, or flaw
detector screen
10
plate
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Piezoelectric Transducer
A transducer is a device that converts energy from one form to
another. Presently, piezoelectric material is commonly used as a
basic component of transducers. A piezoelectric element is a
crystal which delivers a voltage when mechanical force is
applied between its faces, and it deforms mechanically when
voltage is applied between its faces. Because of these
characteristics piezoelectric element is capable of acting as both
a sensing and a transmitting element. Piezoelectric transducers
have been conventionally used to convert electric signals into
sound wave, or to convert sound wave into electric signals.
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Piezoelectric Transducer
case
Signal wire
Piezoelectric element
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Advantages of Ultrasonic Testing
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Thickness and lengths up to 30 ft can be tested.
Position, size and type of defect can be determined.
Instant test results.
Portable.
Capable of being fully automated.
Access to only one side necessary.
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Limitations of Ultrasonic Testing
 The operator can decide whether the test piece is defective or
not while the test is in progress.
 Considerable degree of skill necessary to obtain the fullest
information from the test.
 Very thin sections can prove difficult.
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Crack Detection
Crack detection is one of the primary uses of eddy current
inspection. Cracks cause a disruption in the circular flow patterns
of the eddy currents and weaken their strength. This change in
strength at the crack location can be detected.
Magnetic Field
From Test Coil
Magnetic Field
From
Eddy Currents
Crack
Eddy Currents
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Two methods of receiving the ultrasound
waveform:
• Reflection
• Through Transmission
Principle:
LEFT: A probe sends a sound wave into a test material. There are two indications, one from the
initial pulse of the probe, and the second due to the back wall echo.
RIGHT: A defect creates a third indication and simultaneously reduces the amplitude of the back
wall indication. The depth of the defect is determined by the ratio D/Ep.
Magnetic particle inspection
• Part is magnetized.
• Presence of a surface or subsurface discontinuity in the
material allows the magnetic flux to leak, since air cannot
support as much magnetic field per unit volume as metals.
• Ferrous iron particles are then applied to the part.
• Particles will build up at the area of leakage and form what
is known as an indication.
Dye Penetrant Inspection
• Penetrant may be applied to the test component by
dipping, spraying, or brushing
• After adequate penetration time, the excess penetrant
is removed, a developer is applied.
• Developer helps to draw penetrant out of the flaw
where an invisible indication becomes visible to the
inspector
1. Section of material with a
surface-breaking crack
that is not visible to the
naked eye.
2. Penetrant is applied to the
surface.
3. Excess penetrant is
removed.
4. Developer is applied,
rendering the crack visible.
Dye Penetrant Testing of a Boiler
At first the surface of the
material that is to be tested is
cleaned by a liquid. The liquid
is called cleaner.
Then a liquid with high surface wetting
characteristics is applied to the surface of
the part and allowed time to seep into
surface breaking defects. This liquid is
called penetrant.
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Dye Penetrant Testing of a Boiler
Then another liquid is applied to pull
the trapped penetrant out the defect
and spread it on the surface where it
can be seen. This liquid is called
deveoper.
Two surface cracks
After Dye Penetrant Testing
there are two surface cracks are
Detected.
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Radiographic Testing
• Short wavelength electromagnetic radiation (high
energy photons) to penetrate various materials.
• The amount of radiation emerging from the
opposite side of the material can be detected and
measured
Form of results from Radiographic Testing
Tube exhibiting no cracking
Tube exhibiting moderate cracking
Tube exhibiting light cracking
Tube exhibiting severe cracking
Corrosion detection in pipelines
Advantages of Dye Penetrant
Testing
 This method has high sensitivity to small surface
discontinuities.
 Large areas and large volumes of parts/materials can be
inspected rapidly and at low cost.
 Indications are produced directly on the surface of the part
and constitute a visual representation of the flaw.
 Aerosol spray can make penetrant materials very portable.
 Penetrant materials and associated equipments are relatively
inexpensive.
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Limitations of Dye Penetrant
Testing
 Only surface breaking defects can be detected.
 Precleaning is critical since contaminants can mask defects.
 The inspector must have direct access to the surface being
inspected.
 Surface finish and roughness can affect inspection sensitivity.
 Post cleaning of acceptable parts or materials is required.
 Chemical handling and proper disposal is required.
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Eddy-Current Testing
Uses electromagnetic induction to detect flaws
in conductive materials.
• Variations in the phase and magnitude of these eddy currents can
be monitored using a second 'receiver' coil, or by measuring
changes to the current flowing in the primary 'excitation' coil.
• Variations in the electrical conductivity or magnetic permeability of
the test object, or the presence of any flaws, will cause a change in
eddy current and a corresponding change in the phase and
amplitude of the measured current.
NDT Technique
Nature of defect
Ultrasonic Testing
Sub-surface, interstitial
Magnetic Particle Inspection
Surface and slightly subsurface discontinuities in
ferroelectric materials
Dye Penetrant Inspection
Surface-breaking defects in all non-porous
materials
Radiographic Testing
Surface, Sub-surface defects
Eddy-Current Testing
Surface, Sub-surface defects (depending on
conductivity)
Conclusion
• NDT techniques provide cost-effective and reliable analysis
under realistic conditions.
• Each NDT technique has certain capabilities and limitations
and often more than one technique is used to cover various
parts.
• Increasing availability of robotic scanners improve the
speed of testing large surfaces, hence minimizing the
testing time.